Gyrometry was based initially on measurements performed by implementing systems based on pendulums and springs. Nowadays, it uses optical systems or matter waves. In this context, Alzar et al. (Garrido Alzar, C. L., Yan, W., & Landragin, A., 2012, March, Towards High Sensitivity Rotation Sensing Using an Atom Chip, High Intensity Lasers and High Field Phenomena, pp. JT2A-10, Optical Society of America) have proposed an on-chip compact gyroscope, using matter waves propagating in a circular magnetic guide, called waveguide by analogy with an electromagnetic waveguide. Rotational measurements on this type of device are performed by utilizing the Sagnac effect. The phase shift θ, induced by the Sagnac effect, between two counter-rotating matter waves in a reference frame rotating at the angular velocity Ω, is given by
                    θ        =                                            2              ⁢              Am                        ℏ                    ⁢          Ω                                    (        1        )            where A is the area contained in the waveguide, m the mass of the atoms and h the reduced Planck constant. Utilizing the atomic Sagnac effect described above constitutes a technological breakthrough in the field of gyrometers that traditionally use the optical Sagnac effect: the ratio between the atomic and optical Sagnac phase shift is given, all other factors remaining the same, by the quantity mc2/hv and is of the order of 1010 or 1011 depending on the type of atom and the optical frequency v under consideration. In the device disclosed by Alzar et al., ultra-cold atoms are confined within a circular magnetic waveguide. This device enables a long interrogation time of the atoms (greater than one second) and a dispersion of the propagation velocity that is small enough to utilize the interference fringes of atomic clouds during a measurement. Depositing conductive wires in a manner printed or deposited on the substrate of the chip is a typical method for producing a magnetic waveguide. Such depositions entail surface roughness, which is passed on to the morphology of the waveguide. This element constitutes a major technical problem. Specifically, when guiding cooled atoms in the waveguide, the atoms may encounter these variations that are linked to the surface roughness of the chip. From a wave mechanics viewpoint, one part of the atom may be reflected and the other transmitted, this having the effect of considerably increasing the dispersion of the cooled atoms in the waveguide, and thus potentially making it impossible to measure the Sagnac effect.
Typically, a CCD camera is used to spatially measure the density of atoms in the region of interference formation. This method requires an optical device designed for microscopy; this type of assembly is hardly compatible with embedded and/or compact applications.
Document CN102927978 describes an atomic on-chip ultra-cold atom sensor comprising two microwave waveguides 10 and 11 that are parallel with one another in a direction x, two conductive wires 8 and 9, also in the direction x and arranged on each side of the waveguides, and a plurality of n conductive wires g1, g2, . . . , gn in a perpendicular direction y, as illustrated in FIG. 1.
Ultra-cold atoms having two internal states |a> and |b> are generated.
The combination of the potentials created by the waveguides and the conductive wires, in combination with the homogeneous magnetic field, is supposed to create two potential minima constituting two ultra-cold atom three-dimensional traps, one trap for each internal state. The various currents that are applied make it possible to move the traps along a path that is taken in one direction by one of the traps corresponding to the atoms in one internal state, and in the other direction by the second trap corresponding to the atoms in the other internal state.
In order for the device to operate correctly, it is necessary firstly for the two states |a> and |b> of the interferometer to superpose coherently.
Secondly, it is necessary for the two potential minima to have exactly the same level so as not to include, in the phase term measured by the interferometer, a dependence with the difference in level between the two potential minima. It is also necessary for the two potential minima to have the same curvature so as to keep a coherence time of the interferometer greater than the duration of the interferometric measurement; specifically, in the context of using thermal ultra-cold atoms, the coherence time is inversely proportional to the difference in curvature between the two potential minima.
The wire topology described in FIG. 1 of document CN102927978 does not readily make it possible to obtain two identical potential wells (equality of the curvatures and of the minima of the potentials). Specifically, the presence of the two wires 8 and 9 means that it is necessary to perfectly equalize, with very high precision, the DC currents flowing through them in order to obtain two identical wells.
The wire topology (set of 8, 9 and gi) described in FIG. 1 of document CN102927978 does not make it possible to create a trap that is sufficiently confining along the y-axis of FIG. 1 to enable effective cooling of the atoms and movement of the traps along the y-axis in a time that is shorter than the coherence time of the atomic source that is used.
The wire topology (set of wires 8, 9 and gi) described in FIG. 1 of document CN102927978 creates a magnetic trap with a minimum having a zero magnetic field. This has two consequences on the operation of the sensor:                Atomic losses through the Majorana effect during the phase of cooling the atoms; very few atoms are therefore available at the end of the cooling, resulting in a very low signal-to-noise ratio.        As the two states of the interferometer are two Zeeman sub-levels and, at a magnetic field zero, all of the Zeeman levels are degenerate, it is impossible to achieve an acceptable coherent superposition between the two states of the interferometer and therefore to initialize the sensor.        
Thus, the conductive wires/microwave waveguide configuration from document CN102927978 exhibits numerous drawbacks. The invention aims to fully or partly overcome the technical problems and drawbacks linked to the wire topology in the abovementioned document.